痛い (itai) means "painful" or "sore." It's an い-adjective used to describe physical discomfort or pain in a part of your body. For example, if your head hurts, you can say "頭が痛いです。" (Atama ga itai desu.) which means "My head hurts."

「痛い」は体に痛みがある時に使います。例：頭が痛い。